1. Field of the Invention
The present invention relates generally to a color cathode ray tube and more particularly to a supporting device for an electron beam selecting mask of a color cathode ray tube.
2. Description of the Prior Art
In a color cathode ray tube, as, for example, shown in FIG. 1 which is schematically a longitudinal cross-sectional view and FIG. 2 which is an inside rear view, an electron beam landing position selecting means 4 such as an aperture grille or a shadow mask is disposed in opposed relation to a color phosphor screen 3 formed on the inner surface of a panel portion 1p of a tube envelope 1 to allow an electron beam b (only one beam b is typically shown in FIG. 1) emitted from an electron gun 5 to land on the phosphor screen 3 at its corresponding color phosphor. Such electron beam selecting means 4 has a frame 6 which consists of opposing frame members 6a and 6b and left and right arms 6c and 6d which are supported therebetween at their both ends as, for example, shown in FIG. 3. On the front side of the opposing frame members 6a and 6b of the frame 6, namely, the end surface thereof facing to the color phosphor screen 3, a large number of metal bands 7 are arranged and stretched in parallel to each other between the adjacent metal bands 7. To the frame 6 of the electron beam selecting means 4 thus formed, are attached springs, for example, three springs 9b, 9c and 9d to dispose the frame 6, accordingly, the selecting means 4 inside the panel portion 1p of the tube envelope 1 in facing relation to the phosphor screen 3. The springs 9b, 9c and 9d are each formed by leaf springs and welded at their one end to, for example, the lower frame member 6b and the left and right arms 6c and 6d of the frame 6. Triangular engaging apertures 10 are respectively formed through the springs 9b, 9c and 9d at their free end portions and ceramic stud pins 11 fixed by fritting or the like on the inner surface of the skirt portion of the panel portion 1p, to which the frame member 6b and the arms 6c and 6d of the frame 6 are faced, are engaged into the engaging apertures 10 to settle the position of the frame 6.
Generally, such electron beam selecting means 4 is held to the tube envelope 1 by simply engaging the springs 9b, 9c and 9d, which are all fixed to the three sides of the frame 6 of the selecting means 4, namely, the lower frame member 6b and the left and right arms 6c and 6d, with the corresponding stud pins 11. In this case, the free ends of three members comprising the springs 9b, 9c and 9d are resiliently pressed against the corresponding stud pins 11 toward their base sides having large diameters, so that the respective sides of each triangular engaging aperture 10 are caused to contact with the peripheral surface of the corresponding stud pin 11 at three points, thus the selecting means 4 being held in a predetermined positional relation relative to the tube envelope 1.
With the color cathode ray tube having such structure or particularly color cathode ray tube having an adjusting mechanism such as a bimetal mechanism or the like for adjusting the fluctuation of bar height due to temperature change in connection with the electron beam selecting means, there is such a risk that when the engaged position of the spring 9 (9b, 9c and 9d) with the stud pin 11 is displaced by adjusting the bar height with the bimetal mechanism or is displaced by an external impact, engagement between the spring 9 and the stud pin 11 is disengaged or cannot be restored to a predetermined engaged position so that the positional relation between the phosphor screen 3 and the electron beam selecting means 4 is displaced thus color misregistration or the like being caused.